1. Introduction

Many aspects of Canada’s infrastructure, economy, and ecology are directly affected by climate variability and change. Observations provide information about historical climate and therefore the ‘baseline’ against which future change is compared. Future climate change information, needed to assess future impacts, plan adaptation measures, and develop mitigation policy, cannot be reliably obtained by extrapolation of observed historical changes. Quantitative longer-term applications of climate information require model-based projections driven by a range of greenhouse gas emission scenarios. This document provides a brief overview of the most up-to-date analysis of historical climate observations and future climate projections focusing specifically on Canada. The information presented here builds upon, and is fully consistent with, the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) Working Group I (IPCC, 2013). The current document is intended as a resource for dissemination of climate information with a specific focus on historical and future climate change across Canada. It is not intended to serve as a definitive reference or complete characterization, and readers are directed to the underlying data sources for more detailed and quantitative analyses specific to their climate impact, adaptation, or environmental assessment context.

Given the range of natural climate variability and uncertainties regarding future greenhouse gas emission pathways and climate response, changes projected by one climate model, or one individual emission scenario, should not be used in isolation. Rather, it is good practice to consider a range of projections from multiple climate models (ensembles) and emission scenarios. Although this does not allow one to estimate the probability of a particular climate change scenario, it does convey to users some of the uncertainties involved.

Along the same lines, one should not rely on an individual study or publication to inform on the potential impacts of climate change in Canada. Rather, it is the synthesis of information from a range of valid sources that forms the foundation for understanding climate change and quantitative impact assessment. Information presented in this document is based upon the peer reviewed scientific literature and major climate assessments available to date. The underlying data is publicly available and sources are noted.

Additional information on the use of climate scenarios has been produced for the Canadian adaptation community by the Ouranos Consortium on Regional Climatology and Adaptation to Climate Change (Charron, 2014). This publication may be valuable to those looking for further technical details and guidance on the use of climate scenarios.